The present invention relates to an apparatus for reducing the transmission of engine induced vibration to the drive line. Such an apparatus is the subject matter of the commonly owned, earlier filed U.S. application Ser. No. 829,508, filed on Feb. 14, 1986 and now U.S. Pat. No. 4,724,719. The apparatus described in that application has a split flywheel, with the two flywheel elements arranged on the same axis. The flywheels are drivingly connected to one another by a spring mounting. One of the flywheels is connected to the engine, while the other flywheel is connected to the transmission. An abutment of the spring mounting allocated to one of the flywheel elements is arranged on a second abutment that is frictionally connected to this flywheel element. The second abutment is drivingly connected to the flywheel element, without limiting the rotational capacity of the second abutment relative to the flywheel element, while the strength of the frictional connection is greater than the maximum torque of the engine.
The drive system of a motor vehicle can be designed such that the resonant frequency if at all possible lies somewhat below the idling speed of the engine. Consequently, the resonant frequency is excited virtually only when starting the engine. Thus, travel operation is performed in the so-called hypercritical range, so that the frequency of the vibrations occurring in travel operation is generally considerably higher than the resonant frequency. Only relatively low vibrational amplitudes occur between the device or flywheel elements during travel, a transmission of the vibrations from the engine to the drive line or vice versa being prevented by the spring mounting between the flywheel elements. If, when starting the engine, the resonant range of the device or of the flywheel is run through, the device or flywheel elements execute comparatively large displacement movements relative to one another. However, these movements are effectively damped because the forces transmitted by the spring mounting between the device or flywheel elements exceed the strength of the frictional contact, so that the abutment part frictionally connected to a particular device or flywheel element slips relative to that element.
As long as the forces transmitted between the device or flywheel elements by the spring mounting--such as during the travel of a vehicle--are lower than the strength of the frictional contact, the spring mounting cannot exert any damping effect. This is desirable in the case of the relatively small displacement vibrations that occur in the hypercritical range. However, there are situations in which larger relative movements between the device or flywheel elements can occur even outside the resonant frequency of the drive line. This happens, for example, in the load change between coasting and drive of a vehicle. As the forces occurring in such a load change are often less than the strength of the frictional contact, a damping of the vibrations associated with the load change is not readily possible.
It is therefore an object of the invention to design an apparatus of the initially-mentioned type so that relative movements occurring between the device or flywheel elements are already effectively damped when the forces acting between the device and the flywheel elements in these relative movements are weaker than the maximum engine torque, but stronger than a threshold value to be specified. The maximum engine torque is a predetermined maximum rated engine torque for a particular engine.
This and other objects are achieved by a spring mounting with first and second abutments. The first abutment is frictionally connected with limited rotational capacity to the second flywheel element, while the second abutment, which is arranged on the first abutment, is frictionally connected to the first flywheel element. The frictional contact between the first abutment and the second flywheel element is smaller than the frictional contact between the second abutment and the first flywheel element.
The present invention allows one of the abutment parts to yield or break away even with relatively small torques, and consequently damp relative movements between the device or flywheel elements comparatively early. Only when there are very strong torques or extremely high vibration amplitudes of the relative movements between the device or flywheel elements does the other abutment also yield with a corresponding damping effect.
Thus, the invention ensures a progressive damping of the relative movements of the device or flywheel elements, so that the damping increases with increasing relative movements.
According to a preferred embodiment of the invention, the progressivity can be further improved by each abutment part being frictionally connected to one or both flywheel elements via one or more clutches affected by clearance, the clutches having in each case a different clearance so that, when there is correspondingly strong relative movement of the device or flywheel elements, the effects of the clutches come into action successively with corresponding increase of the respective frictional contact between the abutment part and the particular device or flywheel element.
In a further preferred embodiment of the invention, the abutments are annular discs, radially overlapping one another and having, in the overlap region, cut-outs or windows extending in peripheral direction and overlapping one another which accommodate helical compression springs which are arranged in peripheral direction. The face ends of the springs--seen in axial view--each passes through the planes of the disc. The annular discs forming the first abutment are frictionally connected in the region of their inner periphery by means of coupling laminae to the one device or flywheel element, while the annular discs forming the second abutment are frictionally connected in the region of their outer periphery by means of coupling laminae to the other device or flywheel element. This achieves a space-saving and easily assembled design.
At the same time, it is advantageous if the annular discs forming the first abutment in preferred embodiments have on their inner periphery radial projections which interact in the manner of stops, with clearance in peripheral direction, with counter-projections on the one device or flywheel element or a hub part of the same. It is also advantageous if the annular discs forming the second abutment have on their outer periphery corresponding projections which interact in the manner of stops, with clearance in peripheral direction, with counter-projections which are arranged on the other device or flywheel element or a peripheral rim of the same. In this way, the limited mobility of one of the abutment parts with respect to the allocated device or flywheel element can be ensured very simply.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purposes of illustration only, an embodiment constructed in accordance with the present invention.